Thermocouple wattmeter



July 7, 1953 E. c. GREGG, JR 2,644,923

I THERMOC'OUPLE WATTMETER Filed July 6, 1950 F|G.I.

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I3 l6 l6 I6 INVENTOR' EARLE 0. GREGG, JR.

ATTORNEYS Patented July 7, 1953 THERMOCOUPLE WATTMETER Earle C. Gregg, J12, East Cleveland, Ohio, assignor to the United States of America as represented by the Secretary of-the Navy.

Application July 6, 1950, SerialNo. 172,258.

4 Claims. 1'-

The present invention relates to a thermocouple wattmeter and more particularly to a wattmeter which is capable of measuringhigh frequency electrical power.

The measurement of high frequency electrical power is entirely beyond the capabilities of' the ordinary wattmeters which are strictly low frequency devices. In the past, most power measuring circuits initially depended on impedance and current (or voltage) measurements for determining the power into a load device. Since the impedance of many load devices changes with power, these determinations, based'on impedance bridgetests at very low levels; could at best only give approximate results. The need-consequent- 1y, was great to have a means for measuring the actual power input directly. To take care of these needs the present circuit, known as a thermocouple wattmeter, has been developed for the measurement of power over a large frequency range.

The present invention, in addition to power measurements, has the further advantage of being able also to measure current and. voltage separately. These two measurements, in com. junction with observations of the power, allow a calculation of the load impedance. Another advantage of the invention isthe feature whereby the power range switch tends to keep the impedance constant.

Not only is the. invention direct reading, but the wattmeter will read total power. independent of waveform andhas three power ranges; name- 1y, 100 watts, 500 watts, and 1000 watts full scale.

The calculated and measured scale factors agree within 1.5 percent over thefrequency range from to I00 kc. and themete-r is designed to operate for load impedances in the range from ohms to 300 ohms.

An object of the present invention is the provision 01 a direct reading. wattmeter for measuring power at high frequencies. 7

Another object is to provide a wattmeter which not only measures power, but will also measure. current and voltage separately.

A further object is to provide a wattmeter. which maintains its impedance substantially constant for all ranges.

A final object of the invention is the provision of a wattmeter which by measuring power,- current, and voltage permits the calculation of the. load impedance.

Other objects and features of the invention. will become apparenttothose skilled. inthe art as. the disclosure is made in the fol1owing de-- tailed description of a preferred embodiment of the invention as illustrated inthe accompanying drawings in which:

Fig. 1 is a schematic diagram of the circuitofthe invention.

Fig. 2' is a functional diagram showing the circuit elements utilized when measuring power.

Fig. 3 is a diagram showing which circuit ele- .ments are used to measure current alone.

Fig. 4 is a diagram-showing which circuit elements are used tomeasure voltage alone.

Referring now to the drawings wherein like reference characters designate like or corresponding parts throughout the several views there is shown in Fig. 1 a potential circuit H supplying a load l2. Connected into a circuit II for measuring the power taken by load 12 as well as its voltage and current is the wattmeter of the present invention wherein a thermocouple l3 hasone of its electrodes connected in series with 'a similar electrode H: of a second thermocouple IB, there also being in series with electrodes l4 and I5 a microammeter l7. 7 The meter I! may be calibrated. to read directly in Watts, volts, or amperes depending upon which of these quantities is being measured.

Directly connected to the second electrode 18 of thermocouple I3 is a two-position switch2l whichis arranged to measure power in one of its" positions and voltage and current in the other position. In series with switch 21 is a:four-position' switch 22- which acts to connect any one of. theparallel range resistors-23 to power line 24.

The second electrode 25 of thermocouple i6 is directly connected to a two-position switch 26 Whichmay connect the themocouple 16 directly to power line 24 in one position or else to a fourposition switch 21' in the other position. Switch 21, in turn, is used to select one of the parallel rangeresistors 28, the. common end of which is joined to power line 24.

Also directly connected to electrode 25, of ther-. mocouple I6, is a second two-position switch 3!, which,. it is to be noted, is ganged together with switches 2| and 26. One position of switch 3! is directly tied to line 32 which is joined to electrode [8' of. thermocouple I3, while the other position of the switch goes to the arm of another two-position switch 33. Switch 33. acts to connect' switch 31 to line 32 when voltage across the load 12 is being measured, or else to connect switch 3! to four-position switch 34 when cur-' rent through load I2 is being measured. *It isto be: noted that switch 34 is similar to switches 22 and 21 and: is ganged to them; it acting'to 3 select one of the parallel range resistors 35, the common terminal of which is tied to power line 24 where it joins the common terminal of resistors 23. Placed in series, in the line 24, and positioned between the connections to resistors 23 and 28, is a small shunt resistor 36 whose purpose will be more fully described hereinafter.

The other power line 31 has joined to it the arm of a fourth four-position switch 38- which, .as can be clearly seen in Fig. 1, is ganged to operate in unison with switches 22, 21, and 34. The purpose of switch 38 is to insert any one of the resistors 4| between line 32 and line 31.

The functional diagrams of Figs. 2, 3, and 4 illustrate which of the circuit components are in operation when the device is used to measure power, current, and voltage respectively, and

these diagrams will be more fully described here inafter.

In operation, when the power delivered to load 100, 500, or 1000 watt ranges are employed, but

for the present description assume that the connections are as shown. Therefore, when power is being measured there is a completed circuit as follows: from line 24 through resistor 23, switch 22, switch 2|, electrode i8, line32, resistor 4|, switch 38' to line 3!, with another branchof the circuit from line 26., resistor 2%, switch 21, switch-26, electrode '25, switch 3!, line 32, to resistor 4!. It is to be noted from Fig. 2 that the power circuit is essentially Y-shaped, with the open legs connected to either side of re sistor 36. If the current in the load I2 is represented by I, and the voltage across l2 as E, then the current through one leg ,of the Y circuit will be equal to-their sum and current through the other leg will be equal to their difference.

Fig; '4 shows the circuit components employed when voltage alone is measured, and in this .sitnation the ganged switches 22, 21 and 34, as well as switch 33, remain in theposition shown. However, ganged switches 21, 23 and 3! are now. shifted to the left. This cuts out thermocouple l3leaving a circuit from line 24 at the right hand endof resistor 36, through switch 23, electrode 25, switch 3i, switch 33, line 32, resistor il, back to line 31. Thermocouple leis now in series with resistor 4| and connected in parallel with load l2 right across the power lines 2 3. and Si, so as to measure the voltage applied to the load;

When the current taken by load i2 is measured the circuit is shown by Fig. 3; and the resistor 33, in series in line 24, acts as a shunt to obtain a small current which is representative of the load current. Here, ganged switches 2|, 25 and,3l,- as well as switch 33, are now activated to the left, with switches 22, 21 and 33 in the position" 4 meansfor measuring power, voltage, and current irrespective of wave form, and at relatively high frequencies. Also that once these elements are known, it is a mere matter of calculation to determine the load impedance. The wattmeter is directreading, possesses a high degree of accuracy and represents a marked improvement over similar instruments in the prior art.

"It should be understood, of course, that the foregoing disclosure relates to only a preferred embodiment of the invention and that it is intended to cover all changes and modifications of the example of the invention herein chosen for the invention as set forth in the appended claims.

I What isclaimed is:

1. In combination with a power circuit, a resistor inseries with a first power lead, a pair of thermocouples for producing a current proportional to the power; one electrode-of each thermocouple being connected in series through an indicator, one terminal of the second electrode of each thermocouple being connected to an adjustable resistor respectively, each of said adjustable resistors being connected to a difierent end of the series resistor in the first power lead, the second terminals of said second electrodesconnected together to a thirdadjustable resistor, and said third adjustable resistor being connected to the second power lead, whereby said indicator gives a measure of the power.

2, The power circuit of claim 1 wherein there is provided a fourth adjustable resistor connected between; said first power lead and said second.

electrodes, and switches which act to cut out one thermocouple and a portion of the adjustable resistors when said indicator indicates current in the circuit.

3. The power circuit are switches which act to cut out one thermocouple and a portion'of the adjustable resistors thermocouples each having a heater element and a current generating electrode, a current indicating device in series connection with said current generating electrodes, a first resistor adapted to be connected in series with one lead from a power source to a load, a firstgroup of resistors having an end of each resistor commonly connected to one side of said first resistor,

a second group of resistors having an end of each resistor commonly connected to the other side of said first resistor, a third group of resistors hav ing an end of each resistor commonly connected to said one side of said first resistor, first switching means comprising a first set of ganged singlebladed multi-poled switches, a plurality of said switches having their poles respectively associated with the other ends of said resistors of the three said groups of resistors, second switching means comprising a set of ganged switches for connecting and disconnecting said blades of said first switching means to one side of said heater elements, further resistor means connected to the other side of one of said heater elements and adapted to be tied to a return lead from said load to said power source, through a switch of said first. switching means, a single switch for connecting together a switch of said first and of claim 1 wherein there 5 6 second switching means, said single switch and Number Name 7 Date a pair of switches of said second switching 2,059,594 Massa Nov. 3, 1936 means being connected for selectively connecting 2,277,365 Michael Mar. 24, 1942 a side of the second of said heater elements to 2,316,153 Brown Apr, 13, 1943 said further resistor means or to said third group 5 2,512,927 Freas June 27, 1950 of resistors, one of said pair of switches being connected for connecting the last said side of OTHER REFERENCES said second heater element to said other side Publicatifin 1 RCA Reprint from Proceedings of said first resistor, 0f the IRE, August 1943, Direct Reading Watt- EARLE c, GREGG, 10 meters for Use at Radio Frequencies, page 404,

' Fig. 3.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 15 1,586,533 Peterson June 1, 1926 or V 

